1. Field of the Invention The present invention relates generally to an improved method and apparatus for mixing dry particulate materials with a liquid and, specifically to an apparatus and method for mixing dry cement with water to form a well cementing slurry.
2. Description of the Prior Art
Many different types of chemical processes and other industries require mixing dry particulate materials with liquid to produce a working fluid or slurry product. For instance, well casings penetrating subterranean formations are cemented with a slurry formed from dry cement and water. Typical prior art well cementing systems have featured mixing modules, some of which have included vortex type mixers. In one type vortex mixer, the cement particles are directed downwardly through a vertical pipe section which opens into a pump volute casing. As the cement drops into the volute casing, it is contacted by water, the water being directed downwardly through an outer pipe section which encloses the "cement" pipe and which also opens into the volute casing.
U.S. Pat. No. 4,007,921, issued Feb. 15, 1977, to Zingg, describes a prior art mixing device in which the volute casing and lower end of the concentric pipe sections are supported inside a holding tank. As the slurry mixture leaves the pump volute, it is contained within the holding tank. From the holding tank, part of the slurry is continuously recycled through a densimeter and a recycling pump and back through the pump volute. At the same time, the remaining part of the slurry is directed from the recycling pump to a high pressure cement pump and into the well bore.
Although systems of the type described have been used successfully in well cementing operations, a need exists for a mixing apparatus and method which allows greater control over slurry density than was achieved in the past.
A need exists for such a system which will continuously average the slurry density to produce a more uniform slurry for improved well cementing operations.